Conventionally, in this type of motor drive unit for driving a plurality of motors at once, it was a normal practice to control a plurality of inverter circuits and a plurality of motors separately from one another. For example, such unit is disclosed in Japanese Laid-Open Patent Application No. 2002-165476.
This motor drive unit of conventional system, in which the period of pulse width modulation (hereinafter abbreviated as PWM) of a plurality of inverter circuits is controlled independently of one another and the motor current detecting timings are different, had such problems as large motor current detecting error due to switching noise of the inverter circuits, difficulty of a wide range of vector control or of estimation of rotor position by detection of current.